/*******************************************************************************
 * SAT4J: a SATisfiability library for Java Copyright (C) 2004-2008 Daniel Le Berre
 *
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Alternatively, the contents of this file may be used under the terms of
 * either the GNU Lesser General Public License Version 2.1 or later (the
 * "LGPL"), in which case the provisions of the LGPL are applicable instead
 * of those above. If you wish to allow use of your version of this file only
 * under the terms of the LGPL, and not to allow others to use your version of
 * this file under the terms of the EPL, indicate your decision by deleting
 * the provisions above and replace them with the notice and other provisions
 * required by the LGPL. If you do not delete the provisions above, a recipient
 * may use your version of this file under the terms of the EPL or the LGPL.
 * 
 * Based on the original MiniSat specification from:
 * 
 * An extensible SAT solver. Niklas Een and Niklas Sorensson. Proceedings of the
 * Sixth International Conference on Theory and Applications of Satisfiability
 * Testing, LNCS 2919, pp 502-518, 2003.
 *
 * See www.minisat.se for the original solver in C++.
 * 
 *******************************************************************************/
package org.sat4j.minisat.restarts;

import org.sat4j.minisat.core.RestartStrategy;
import org.sat4j.minisat.core.SearchParams;

/**
 * Luby series 
 */
public class LubyRestarts implements RestartStrategy {

    /**
     * 
     */
    private static final long serialVersionUID = 1L;

    private static int[] cachedValues = new int[] { 1, 1, 2 };
    
    public static final int luby(int i) {
        if (i>=Integer.MAX_VALUE/2) {
            throw new IllegalArgumentException("i is too big");
        }
        if (i >= cachedValues.length) {
            int oldsize = cachedValues.length;
            int newsize = i<<1;
            int[] newContent = new int[newsize + 1];
            System.arraycopy(cachedValues, 0, newContent, 0, oldsize);
            int nextPowerOfTwo = 1;
            while(nextPowerOfTwo<=oldsize)
                    nextPowerOfTwo <<= 1;
            
            int lastPowerOfTwo = nextPowerOfTwo >> 1;
            for (int j = oldsize; j <= newsize; j++) {
                if (j + 1 == nextPowerOfTwo) {
                    newContent[j] = lastPowerOfTwo;
                    lastPowerOfTwo = nextPowerOfTwo;
                    nextPowerOfTwo <<=1;
                } else {
                    newContent[j] = newContent[j - lastPowerOfTwo + 1];
                }
            }
            cachedValues = newContent;

        }
        return cachedValues[i];
    }

    static {
        // precompute 64 first values
        luby(32);
    }

    private int factor;

    private int count;

    public LubyRestarts() {
        setFactor(32); // uses TiniSAT default
    }

    public void setFactor(int factor) {
        this.factor = factor;
    }

    public int getFactor() {
        return factor;
    }

    public void init(SearchParams params) {
        count = 1;
    }

    public long nextRestartNumberOfConflict() {
        return luby(count) * factor;
    }

    public void onRestart() {
        count++;
    }

    @Override
    public String toString() {
        return "luby style (SATZ_rand, TiniSAT) restarts strategy with factor "
                + factor;
    }

}
